Find Secret Cars:
To find secret cars, search for the paint cans marked with ????. Going through the can will unlock the car.

Pencil-Drawn Mode:
In Paris, go to the Musee du Louvre and drive up to one of the glass pyramids. Press up on the right analog stick to look at it. Hold your stare for 30 seconds and the screen will have a textured look, and everything will look like it's sketched on.

Super Sonic Mode:
When in Washington DC find the Lincoln Memorial and pull up to his feet. Using the right thumb stick, look up at him and hold it there for 20-30 seconds. The screen should go black and white. Drive away and you will notice that you are in super sonic speed mode.